Exhaust Manifold.

[Ruan]

The nozzles are good to 200bhp on an appropriate pump.

Yes RP is high, but that is irrelevant.

RP is a function of how much flow you want to get into the engine and how big the nozzle is.

You could run huge nozzles and low RP, or high RP and small nozzles.

But you can't get BOTH without a BIG pump... and that is the problem, the pump.


The standard HDi pump is good to maybe 180bhp assuming all else is good, at about 4000rpm.

Big injectors, small ones, twice as many, it won't make any difference. No combo of rail pressure and tip size will get around the fact the pump just can't flow enough fuel for more power, no matter how it's injected.


So injectors, yes upgrade them, but only when you have a better pump too.


The old XUD pump is different. They can flow LOADS of fuel. The issue is they probably have higher parasitic losses due to being over-specced a lot of the time.
To a certain extent bigger nozzles are less precise, so over-sizing won't give exact injections at low IQ's, so idle and cold-starting and precise emissions control are less feasible.

Not saying that is bad, if power is what you want great, I personally live the XUD9 when tuned up!

But the HDi is different in a lot of ways, and beyond the small turbine on the stock turbos causing torque curves like mountains and peak power at ~ 3500rpm or below, the next problem is the HP pump!

Dave

This is where I 100% disagree...

The more pressure being produced, the more the flow rate will drop, the more power that is consumed and the more heat is produced...

A bigger pump will move MORE fuel at MORE pressure with LESS heat requiring less power due to inefficiencies...

Just in the same way as you can stick more RP at injector nozzles but you eventually get to a point where you can stick more and more pressure at them, but it's a law of diminishing returns, your injectors will continue to stay open for longer to flow the required amount of fuel - the RP keeps on rising at an exponential rate for little return - hence bigger nozzles required...

Big nozzles YES they do reduce refinement and reduce the resolution at which you can control the engine, but after experiencing VE/VP TDis with CHRONIC nozzles and seeing PD TDis with rediculous nozzles - they really are NOT the issue that people make out, I've seen injectors that are good for 400hp and they give a CLEAN, SMOOTH idle, no starting issues, no haze midrange or anything like that... But will happily let through MASSIVE quantities of fuel, all at SIGNIFICANTLY lower pressures than HDis can run at, the resolution and precision of EDC15 will happily cope with the nozzles given the mapping is good...

This is a flow chart for a positive displacement fuel pump, it's a lobe pump, but positive displacement same as a piston pump so explains my point perfectly -



With regards to the XUD pumps, they cannot flow a significant amount of fuel in stock form, but they are a completely different kettle of fish, with Indirect injection the nozzle is barely a restriction at all, they aren't VCO like HDi nozzles and the pressure is only built up by the spring and shim stack unlike HDis where it's built in the rail - you can build however much or little you like... But we know what happens with DI nozzles and trying to increase IQ on VE pumps - the line pressure builds and builds and the injection length gets longer to a point where you start damaging the pump etc because the fuel won't get through the nozzles fast enough... The pump itself is probably OK sure, but again, nozzles are the cause of the problem - bigger nozzles = less line pressure = more fuel over a shorter period of time, but you do get to the point where even the pump cannot cope - hence bigger injection heads to reduce duration, which means more flow, less time...

Even past all of this, you'll still get to a time where the OEM pump cannot cope, so bigger pump, bigger nozzles - off you trot... Keep the power up at 5000rpm and bring the torque in gradually, just because it "feels" epic to have that lovely wadge of torque at 1800rpm, it simply rapes clutches, doesn't do much for the big ends and rods etc, I personally rekon you could keep the torque lower and still even stay on an "uprated" clutch, maybe not stock, but no need for jerky, heavy paddle clutches...